The present invention relates to a method and apparatus for making and developing ionographic images of X-rayed objects. More particularly, the invention relates to improvements in a method and apparatus for reducing or eliminating the effects of stray radiation on the quality of visible images which are obtained as a result of development of latent images on dielectric receptor sheets of the type used in ionography imaging chambers.
It is well known that stray radiation which develops on exposure of an object to X-rays adversely influences the contrast of the latent image, i.e., of a pattern of electrostatic charges on a dielectric receptor sheet in the gas-filled interelectrode gap of an ionography imaging chamber which is located in the path of X-rays that have penetrated through the object. Attempts to reduce or eliminate the effects of stray radiation upon the quality of the latent image include the provision of rasters which are placed between the object and the imaging chamber and serve to absorb stray radiation while permitting primary radiation to pass therethrough and to reach the receptor sheet in the interelectrode gap. Such rasters are also used in radiographic apparatus wherein the object-modulated X-rays produce an image on photographic film. A drawback of rasters is that, in addition to absorbing stray radiation, they also absorb a high percentage (approximately 50 percent) of primary radiation. Consequently, the dose of X-rays to which the object is exposed must be increased accordingly, i.e., by a value corresponding to the absorption factor of the raster. This is highly undesirable in certain fields of radiography, especially when the object to be exposed to X-rays is a selected part of a patient's body. Another serious drawback of rasters is their extremely high cost, especially when the size of a raster matches the size of the receptor sheet (this is the customary way of selecting the size of conventional media which absorb stray radiation).